The present invention relates to an image forming apparatus capable of forming a toner image on a sheet-shaped recording medium (hereinafter referred to simply as “sheet medium”) such as plain paper, thick paper, a postcard, an envelope, or an OHP sheet.
An image forming apparatus is known which is equipped with a fuser for fusing a toner image on a sheet medium by causing the sheet medium to which the toner image has been transferred to pass through the fuser while heating it and a sheet ejecting roller pair for ejecting the sheet medium from the apparatus.
In this type of image forming apparatus, a sheet medium tends to curl when it is heated in passing through the fuser. If the sheet medium is ejected as it is, it may be rounded at an ejecting section (e.g., sheet ejection tray). Or the leading end of a curled sheet medium may hit an already ejected sheet medium and push out the latter from the ejecting section (e.g., sheet medium ejection tray).
One conventional countermeasure against the above phenomenon is disclosed in Japanese Patent Publication No. 60-171963A. The sheet ejecting roller pair is formed by plural drive rollers that are spaced from each other and fixed to a drive shaft and follower rollers that are the same in number as the drive rollers and are brought into pressure contact with the drive rollers. Each roller of one of the two sets of rollers is provided with a large-diameter flange at both ends and a corresponding one the other set of rollers goes into the space between the flanges. As a result, a sheet medium being ejected is waved when viewed from the ejecting direction and thereby made stiffer (rollers for waving a sheet medium when viewed from its ejecting direction in this manner are called corrugation rollers). The sheet medium is thus prevented from being curled.
In the above apparatus, the sheet ejecting roller pair itself is given the function of waving a sheet medium; that is, the ejecting roller pair is configured so as to wave a sheet medium by its pressure contact force. Since the purpose of the sheet medium ejection pair is to eject a sheet medium, the pressure contact force of the rollers constituting the sheet ejecting roller pair needs to be strong enough to eject a sheet medium reliably irrespective of its type. This results in a problem that when a synthetic resin sheet medium is ejected after being heated by the fuser, the waved state may be permanent.
Japanese Patent Publication No. 5-289564A discloses an image forming apparatus in which a door cover is equipped with a roller pair which is disposed downstream of a fuser and transports a sheet medium coming from the fuser. With this configuration, the replacement of the fuser is facilitated and a sheet medium that is jammed in the fuser or a portion downstream thereof can be removed easily.
In this apparatus, the door cover is configured so as to be able to be opened and closed merely by a shaft. Therefore, the accuracy of positioning, with respect to the fuser, of the roller pair which is provided in the door cover tends to be low, which results in a problem that a sheet medium jam is prone to occur.
E-rings are known as stoppers to be attached to a shaft. Generally, the end face of a shaft to which the E-ring is attached is exposed. The exposed end face may be touched by a human hand, for example. Therefore, a state that the temperature of the shaft is high and its end face is exposed is not desirable. For example, the temperature of a shaft close to a fuser of an image forming apparatus becomes high and hence a state that its end face is exposed is not desirable.